One usage for such soldered joints resides in metal hydride reservoirs according to the above-mentioned laid-open application wherein pulverulent metal is stored in a plurality of parallel-connected reservoir pipes. By supplying hydrogen and removing heat, the stored material can be hydrogenated, and hydrogen can be stored. By feeding heat into the reservoir, the thus-stored hydrogen can again be released. Such reservoirs are subjected to great pressure and temperature fluctuations, and for this reason the soldered joints are exposed to high stresses. Problems are encountered in the production of hydrogen-impermeable soldered joints in case of passive austenitic structural steel parts, especially if the latter contain titanium.
Nickel solders containing boron and silicon exhibit, due to their reactivity, a good wetting characteristic on austenitic materials. Under a hydrogen atmosphere, such nickel-base solders with only small additions of an alloying element tend to form, with partial hydride formation, intercrystalline fractures of low deformation. Such nickel-base solders are unsuitable for long-term use in hydride reservoirs.
Copper-tin-base solders, due to low hydrogen solubility, exhibit high resistance against becoming brittle by hydrogen, but they show an only limited wetting characteristic on passive austenites, on account of their low reactivity.
German Pat. No. 866,132 describes a brazing method for sintered metal parts of stainless steel wherein, prior to soldering, metal is sprayed onto the soldering points to improve the tensile strength and ductility in the joints of such brittle materials. German Pat. No. 484,494 discloses a brazing method for iron and steel parts wherein the latter are plated by electrodeposition with nickel with a layer thickness of 50-200 .mu.m prior to soldering and are thereafter soldered with a copper or bronze solder. In this process, the solder forms an alloy with the nickel, providing an especially high strength of the soldering point; besides, sluggish flow and a high soldering temperature of the copper or bronze solder are avoided. German Auslegeschrift No. 1,063,010 emphasizes that a silicon component in an alloyed bronze-base solder acts as a deoxidizing agent; other alloy components, especially nickel and silver, provide good flowability.